The present invention relates to a mass spectrometer with an ion source wherein a liquid sample is ionized at atmospheric pressure, and more specifically, a sample introduction device wherein a liquid sample which is a subject of analysis is introduced into the ion source of the mass spectrometer.
In a liquid chromatograph mass spectrometer wherein a liquid chromatograph and a mass spectrometer are combined, in order to generate a gas ion from a liquid sample, generally, an atmospheric pressure ionization method such as an electrospray ionization method (ESI), atmospheric pressure chemical ionization method (APCI) and the like is used. When the object sample is analyzed, a sample introduction tube for the above-mentioned atmospheric pressure ionization mass spectrometer is connected to the end of a column of the liquid chromatograph, and the liquid sample whose components are separated by the chromatography column is introduced to an atmospheric pressure ion source of the mass spectrometer through the sample introduction tube.
On the other hand, in order to calibrate or adjust the mass spectrometer itself, a standard sample whose type and concentration are well-known is required to be analyzed. For that purpose, instead of a sample obtained from the chromatography column of the liquid chromatograph, the standard sample is required to be directly introduced to the ion source. This kind of direct liquid sample introduction method is generally called an infusion method. As an infusion method, a method wherein the liquid sample filled in a syringe is pumped by operations of a syringe pump and introduced to the mass spectrometer, is well-known (for example, refer to Patent Document 1: Japanese Patent Application Publication (TOKKAI) No. H9-159661).
This method is suitable for introducing a relatively small amount of liquid sample. On the other hand, since the liquid sample is required to be sucked into the syringe, or the syringe filled with the liquid sample is required to be set in the syringe pump, the operation takes extra time. A device described in the Patent Document 1 includes a structure which can connect the syringe and a sample container through a diversion valve, so that the above-mentioned operational inconvenience can be resolved. However, the size of the device relatively increases, so that the cost also increases.
On the other hand, as another infusion method, a method of sending the liquid sample by gas pressure is well-known (for example, refer to Patent Document 2: U.S. Pat. No. 5,703,360). FIG. 5 is a schematic structural view of a device which introduces a sample by gas pressure. A liquid sample 71 is retained inside a sealed container 70, and nitrogen gas is supplied to an upper space of the container 70 through a valve 73 provided in a gas introduction channel 72. At this time, the gas pressure inside the container 70 is monitored by a pressure sensor 74, and the opening and closing of the valve 73 are adjusted in such a way that the gas pressure maintains, for example, 100 kPa. The liquid sample inside the container 70 is pushed down by the gas pressure, so that in accordance with this movement, the liquid sample is sent through a sample introduction tube 75 whose one end is soaked (viz., immersed) in the liquid sample 71, and reaches a nozzle 52 of the mass spectrometer.
The above-mentioned method has a simple structure compared to the method using the syringe pump, and since an expensive component is not required, the cost can be moderate. However, relatively large amount of sample is required for a sample introduction. More specifically, in order to apply a pressure in the container 70 and send the liquid sample 71 which is retained in the container 70 as mentioned above, a gas introduction opening and a liquid derivation opening are required to be positioned in a plug portion which blocks the upper surface opening of the container 70. Therefore, structurally, the container 70 is required to have a certain size, and usually, in order to adequately send the liquid, approximately several tens of mL of liquid volume is required.
In the case of an inexpensive sample, the relatively large amount of sample as mentioned above can be easily prepared. However, in the case of an expensive sample or a sample without a standard sample such as a sample obtained by, for example, synthesis, purification, and extraction, in many cases, it is unrealistic to prepare the above-mentioned large amount of sample. Also, there is a sample marketed in a state of being preserved in a small-size vial bottle. If such a sample is preserved in another container or syringe, the sample will be inevitably wasted due to the amount remaining on the inner surface of the bottle or syringe.
The present invention has been made in order to solve the above-mentioned problem, and an object of this invention is to provide a mass spectrometer with a sample introduction device which can introduce a small amount of liquid sample to an ion source without wasting the liquid sample or increasing the cost to manufacture.
Further objects and advantages of the invention will be apparent from the following description of the invention.